In general, a Bayer process is a process of eluting aluminum hydroxide by dissolving bauxite in a caustic soda (NaOH) solution and heating the dissolved solution (dissolving process), removing sludge and then precipitating the aluminum hydroxide dissolved in the caustic soda (precipitating process).
The aluminum hydroxide produced by the Bayer process contains a large amount of impurities due to impurities from the bauxite used in the dissolving process and residues of a sub-material used in the Bayer process. Therefore, alumina having a high degree of purity cannot be prepared by a preparation method including the Bayer process described above.
Techniques for preparing high-purity alumina, which were conventionally used, generally used a method of collecting alumina by dissolving a high-purity aluminum acid containing a small amount of impurities and recrystallizing the dissolved aluminum acid as aluminum hydroxide or vaporizing a high-purity aluminum compound at an ultra high temperature. However, the method has low mass productivity, and its manipulation is difficult. Particularly, a high-priced apparatus and material should be used. Hence, much cost is spent, and product loss, environmental contamination, etc. are caused in a preparation process.